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### When to use De Broglie Equation

Posted: **Tue Oct 17, 2017 10:02 pm**

by **Isabella Sanzi 2E**

I am just wondering under what circumstances that we can use the De Broglie equation. I understand that it solves for wavelength, but why use the de Broglie equation instead of another way to solve for wavelength? Does it simply depend on what information you are given? Also, why doesn't the equation apply to light?

### Re: When to use De Broglie Equation [ENDORSED]

Posted: **Tue Oct 17, 2017 10:08 pm**

by **Emilie Hoffman 1E**

The De Broglie equation equation outlines the idea that things that have rest mass (i.e. something that has weight) can behave like waves through having an oscillating way of moving (like basically they move back and forth over the line of their projected path) and thus wavelength. We can't use this to calculate the wavelength of light because light is by definition massless, which would make this equation perpetually zero. Thus the De Broglie equation is reserved for things that have mass, like electrons or baseballs.

### Re: When to use De Broglie Equation

Posted: **Wed Oct 18, 2017 10:49 am**

by **Elika Asis 3C**

^^^

To elaborate more, De Broglie's equation is typically used when the object's wavelength we are told to look for has mass. On the other hand, if we're dealing with massless particles like photons, we then use c=λν or E=hν. But in my discussion section, we were also told that we could use the c=λν for objects with mass, we just have to replace c (the speed of light) with velocity (not 100% that I worded that correctly though!)

### Re: When to use De Broglie Equation

Posted: **Fri Oct 20, 2017 9:57 am**

by **Varsha Sivaganesh 1A**

Also, when you need to use De Broglie the problem will give you mass and/or velocity, whereas if you were to use the other equation relating wavelength to frequency, they would give you the frequency of the photon.

### Re: When to use De Broglie Equation

Posted: **Fri Oct 20, 2017 10:06 am**

by **Ishan Saha 1L**

In addition to what everyone else has already said, it is important to note that DeBroglie's Eq is reserved for objects that have momentum. An objects momentum (p) is equal to its mass (m) times its velocity (v). This is why DeBroglie's equation has the notation λ=h/p, where λ is wavelength, h is Plank's Constant, and p is momentum.

### Re: When to use De Broglie Equation

Posted: **Fri Oct 20, 2017 1:14 pm**

by **Sydney Briggs 1B**

To add onto this question, is there any way to connect finding the kinetic energy with the de Broglie equation? Since both contain mass, I wasn't sure if they could be used together.

### Re: When to use De Broglie Equation

Posted: **Sun Oct 22, 2017 7:44 pm**

by **Josh Moy 1H**

Use when you have mass and velocity and need wavelength

### Re: When to use De Broglie Equation

Posted: **Sun Oct 22, 2017 8:25 pm**

by **Haocheng Zhang 2A**

I think we can use de Broglie equation to find kinetic energy if we know the wavelength and either mass or velocity of the obeject.

### Re: When to use De Broglie Equation

Posted: **Sun Oct 22, 2017 8:29 pm**

by **Karan Singh Lecture 3**

Debroglie is used for electrons, so one can find their wavelength.

### Re: When to use De Broglie Equation

Posted: **Mon Oct 23, 2017 1:22 pm**

by **Chem_Mod**

Because for real particles you don't have another way to determine the wavelength. And it doesn't apply to photon since a photon doesn't have invariant mass.

### Re: When to use De Broglie Equation

Posted: **Sat Oct 28, 2017 10:39 am**

by **Kai_Chiu 1F**

The De Broglie Equation is used every time velocity and/or mass is given.

### Re: When to use De Broglie Equation

Posted: **Sat Oct 28, 2017 12:46 pm**

by **nanditasundarapandian1D**

De Broglie's Equation is used to get a direct relationship between wavelength and momentum.